Recently, the demand for high-resolution and high-quality images, such as High Definition (HD) images and Ultra High Definition (UHD) images has been increasing in various fields. As the resolution and picture quality of image data becomes higher, the amount of information or amount of bits that are transmitted is correspondingly increased, relative to existing image data. Accordingly, in the case of transmitting image data using a medium such as an existing wire/wireless line, or in the case of storing image data using an existing storage medium, transmission costs and storage costs are increased. In order to solve these problems, high-efficiency image compression techniques may be used.
There are various image compression techniques, such as an inter prediction technique that predicts pixel values included in the current picture from a picture that is before or after the current picture, an intra prediction technique that predicts pixel values included in the current picture using pixel information from the current picture, and an entropy encoding technique that allocates a short codeword to a value having a high appearance frequency and allocates a long codeword to a value having a low appearance frequency. Image data can be effectively compressed to be transmitted or stored using such image compression techniques.